SDAA378 August   2026 ADS125H18

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Detailed Description
    1. 2.1 Understanding ADS125H18 OWCS Operation
    2. 2.2 Using OWCS with Single-Ended Input Signals
      1. 2.2.1 Analyzing OWCS Behavior for Single-Ended Input Signals
      2. 2.2.2 Verifying OWCS Operation with a Single-Ended Input Using the ADS125H18EVM
        1. 2.2.2.1 Verifying OWCS Operation with a Single-Ended Input
        2. 2.2.2.2 Using a Fewer Number of Conversions for OWCS with a Single-Ended Input
          1. 2.2.2.2.1 Unsettled Data for Single-Ended Inputs
          2. 2.2.2.2.2 Settled Data for Single-Ended Inputs
        3. 2.2.2.3 How Input Capacitance Affects OWCS Performance for Single-Ended Inputs
        4. 2.2.2.4 Using the ADS125H18 Programmable Delay to Mitigate Settling Effects for Single-Ended Inputs
    3. 2.3 Using OWCS with Differential Input Signals
      1. 2.3.1 Analyzing OWCS Behavior for Differential Input Signals
      2. 2.3.2 Verifying OWCS Operation with a Differential Input Using the ADS125H18EVM
        1. 2.3.2.1 Verifying OWCS Operation with a Differential Input
        2. 2.3.2.2 Using a Fewer Number of Conversions for OWCS with a Differential Input
          1. 2.3.2.2.1 Unsettled Data for Differential Inputs
          2. 2.3.2.2.2 Settled Data for Differential Inputs
        3. 2.3.2.3 How Input Capacitance Affects OWCS Performance for Differential Inputs
          1. 2.3.2.3.1 Back-to-Back, Differential OWCS Measurements with Input Capacitance
        4. 2.3.2.4 Using the ADS125H18 Programmable Delay to Mitigate Settling Effects for Differential Inputs
    4. 2.4 Using the ADS125H18 Channel Sequencer to Implement an OWCS Algorithm
      1. 2.4.1 Example: Configuring the ADS125H18 Sequencer for the OWCS Algorithm
      2. 2.4.2 Understanding the OWCS Algorithm in the ADS125H18 Example Code
        1. 2.4.2.1 Initialization
          1. 2.4.2.1.1 Initialize the sequencer
          2. 2.4.2.1.2 Enter the "_step" Array Values
          3. 2.4.2.1.3 Analyze the Sequence
        2. 2.4.2.2 Starting the Sequencer and Processing Data
          1. 2.4.2.2.1 Update OWCS Step Values and Calculate "total_conversions"
          2. 2.4.2.2.2 Starting the Sequencer and Taking Data
          3. 2.4.2.2.3 Processing the OWCS Data
          4. 2.4.2.2.4 Using the OWCS Results
  6. 3Summary
  7. 4References
  8. 5Appendix A
    1. 5.1 Using OWCS with Redundant Systems
      1. 5.1.1 Dual, Redundant Systems versus Single-Device Systems
      2. 5.1.2 Using 1x OWCS versus 2x OWCS in a Dual Redundant System
      3. 5.1.3 Error Sources in Dual, Redundant Systems
        1. 5.1.3.1 RA1 and RB1 Errors
        2. 5.1.3.2 RA2 and RB2 Errors
        3. 5.1.3.3 VREF1 and VREF2 Errors
      4. 5.1.4 Measuring Differential Inputs in a Dual, Redundant System
      5. 5.1.5 Dual, Redundant System Summary

2.2.2 Verifying OWCS Operation with a Single-Ended Input Using the ADS125H18EVM

Testing was performed to verify OWCS operation using the ADS125H18 evaluation module (EVM). The ADS125H18 EVM is a platform for evaluating the functionality and performance of the ADS125H18. The ADS125H18EVM-PDK eases the evaluation of the device with hardware, software, and computer connectivity through the universal serial bus (USB) interface. Figure 2-6 shows the ADS125H18 EVM.

ADS125H18EVM Board ImageFigure 2-6 ADS125H18EVM Board Image

The following ADC and EVM conditions were used to perform the OWCS verification:

  • ADS12H18V20
  • Internal 25.6MHz oscillator
  • Speed mode 3 (fMOD = 12.8MHz)
  • Internal 2.5V reference voltage
  • Single-shot sequence mode
  • Two enabled steps (same input channel):
    • Step 1 = OWCS disabled
    • Step 2 = OWCS enabled
  • Three output data rates (ODR):
    • 1.6kSPS (sinc4+sinc1 filter, OSR = 8000)
    • 12.5kSPS (sinc4 filter, OSR = 1024)
    • 50kSPS (sinc4+sinc1 filter, OSR = 256)
  • 512 conversions per OWCS step (to capture possible settling behavior)
  • No external passive (R or C) components